iptables: support SO_ORIGINAL_DST

Envoy (#170) uses this to get the original destination of redirected
packets.

2 files changed, 10 insertions, 2 deletions

diff --git a/pkg/abi/linux/netfilter.go b/pkg/abi/linux/netfilter.go
index a91f9f018..9c27f7bb2 100644
--- a/pkg/abi/linux/netfilter.go
+++ b/pkg/abi/linux/netfilter.go
@@ -59,7 +59,7 @@ var VerdictStrings = map[int32]string{
 	NF_RETURN:      "RETURN",
 }
 
-// Socket options. These correspond to values in
+// Socket options for SOL_SOCKET. These correspond to values in
 // include/uapi/linux/netfilter_ipv4/ip_tables.h.
 const (
 	IPT_BASE_CTL            = 64
@@ -74,6 +74,12 @@ const (
 	IPT_SO_GET_MAX             = IPT_SO_GET_REVISION_TARGET
 )
 
+// Socket option for SOL_IP. This corresponds to the value in
+// include/uapi/linux/netfilter_ipv4.h.
+const (
+	SO_ORIGINAL_DST = 80
+)
+
 // Name lengths. These correspond to values in
 // include/uapi/linux/netfilter/x_tables.h.
 const (
diff --git a/pkg/abi/linux/socket.go b/pkg/abi/linux/socket.go
index c24a8216e..d6946bb82 100644
--- a/pkg/abi/linux/socket.go
+++ b/pkg/abi/linux/socket.go
@@ -239,11 +239,13 @@ const SockAddrMax = 128
 type InetAddr [4]byte
 
 // SockAddrInet is struct sockaddr_in, from uapi/linux/in.h.
+//
+// +marshal
 type SockAddrInet struct {
 	Family uint16
 	Port   uint16
 	Addr   InetAddr
-	Zero   [8]uint8 // pad to sizeof(struct sockaddr).
+	_      [8]uint8 // pad to sizeof(struct sockaddr).
 }
 
 // InetMulticastRequest is struct ip_mreq, from uapi/linux/in.h.